The invention concerns a distributor element, particularly a feed distributor, for metering lubricants like grease for lubricating installations.
A known lubricant distributor of this type features a valve piston with a bore. The valve piston moves under the lubricant pressure operating at a lubricant inlet against the force of a single return spring from a starting position in which the bore releases a connection via a connection passage from a metering chamber to a dispensing chamber, to a metering position in which the valve piston releases a passage from the lubricant inlet to the connecting passage and therefore to the metering chamber. Additionally, this lubricant distributor has a dispensing piston which can be moved against the force of the only return spring under the effect of lubricant entering the metering chamber. As a result of the lubricant pressure building up in the metering chamber, the lubricant volume present in the dispensing chamber between the valve piston and the dispensing piston is pushed into at least one lubricant outlet and the valve piston is moved by the dispensing piston into an intermediate position until pressure equalization has occurred, in which position the valve piston blocks the passage from the lubricant inlet to the connecting passage and therefore to the metering chamber. Upon a subsequent pressure relief at the lubricant inlet the valve piston and also the dispensing piston are returned to their starting position by the only return spring. A disadvantage of such a distributor element is that the hydraulic lubricant pressure (working pressure) of e.g. up to 250 bar operating at the valve inlet, must be reduced to a relatively low residual pressure of e.g. about 45 bar for the required pressure relief to ensure reliable operation.
The known design, in particular if several lubricant distributors are connected in series, can lead to impaired functioning of the last lubricant distributor because of pressure reduction occurring in the lubricant line. The problem of a too low relief pressure cannot be solved by strengthening the only return spring provided in this state of the art, because this does not only cooperate with the valve piston but in the other direction also with the dispensing piston. A stronger return spring would lead to an increase of the pressure which must move the dispensing piston into its final position.